We are attempting to characterize the active alkali metal ion transport system of the isolated silkworm midgut. Presently we are devoting most of our efforts to the kinetic analysis of the system. Preliminary work is underway to isolate the chemical components. The project is viewed as a model for transepithelial ion transport including transport in vectors and as a prospective tool in the control of plant eating insects. We have lingered with the kinetic analysis because we are finding that our steady-state analysis of the kinetics forces us to develop new techniques and concets, and yields results which are inconsistent with old work on the midgut and other epithelial systems. This current year we have determined the dependency of the potassium-pump on pH and potassium concentration, refined our theoretical analysis of influx kinetics, analyzed the counting of alkali metal ions by Cerenkov radiation, calculated the size of the transport pool directly from the data with no assumptions about the model, resolved a controversy regarding the ratio of potassium transport to cesium transport, calculated the size of extracellular spaces kinetically, initiated a study of the coupling of potassium transport to metabolism and have demonstrated that the active transport of potassium is the primary event in the secretion of molting fluid by the isolated integument of pharate pupae.